The present invention pertains generally to measuring and testing systems and more particularly to a monitoring device for a container testing system.
Container testing machines such as the can testing machine disclosed in U.S. Pat. No. 4,074,809 issued to McMillin et al, Feb. 21, 1978, which is incorporated herein by reference and forms a part of this disclosure for all that it teaches, are useful in detecting defects in printed metallic can body members. Can testing devices such as disclosed in the McMillin et al. patent are capable of testing can body members for the presence of printed ink thereon and the presence of defects in the can body member such as cracks, pin holes, etc.
To minimize the scrap rate, i.e., the number of cans rejected by the can testing machine, it is useful to monitor the operation of the can testing machine to identify potential can production process problems and can testing machine problems. For example, it is useful to determine if the can process is producing an excess number of defective cans, in which case the can production process must be checked, or, if some problem within the can testing machine is causing an excess number of rejected cans.
The can testing machine disclosed by McMillin et al in the above referenced U.S. Patent produces control signals representative of detected leaking cans, unpainted cans and empty can pockets within the can testing machine. This can test data is utilized by the can testing machine to perform various control functions. A can test data signal representative of a leaking can or an unpainted can will cause a solenoid to be activated to reject the can into a scrap can box. Detection of an empty can pocket produces a control signal to activate control circuitry within the can testing machine to improve performance of the can testing machine apparatus, as more fully disclosed in U.S. Pat. No. 4,501,366 issued Feb. 26, 1985 by Roger A. Thompson entitled "Photomultiplier Tube Assembly", which is incorporated herein by reference for all that it teaches.
Since the scrap rate has a significant impact upon the economic efficiency of the total can production process, it is useful to determine whether defects have been generated either within the can testing process or in the process of manufacture of the cans. For example, empty can pockets in the can testing machine can result either from track misalignment or production of damaged cans. Similarly, a can will be rejected from the can testing machine in response to an unpainted can signal resulting from a defect in the can painting process or the necessity for adjustment of the unpainted can sensor. Consequently, it is of the utmost importance to determine the nature of the cause of can rejection. If it can be determined, for example, that a flange seal in a particular pocket of the can testing machine is defective, it may be economically justified to stop the can testing machine and repair the flange seal to significantly reduce the scrap rate, especially when it can reasonably be determined that the source of the problem exists in an identified piece of hardware, such as a flange seal in a particular can pocket.
Moreover, it is useful to quantitatively identify the scrap rate as a function of the total number of cans processed. Normally, no quantitative measurement of the number of rejected cans is made. Although it is easy to identify extremely large changes in the scrap rate as a result of a large number of rejected cans, changes in the scrap rate which are not extremely large are many times much more difficult to recognize in the lack of a quantitive measuring device. This is a result of the fact that the can testing machine operates at variable speeds which causes the scrap rate to vary in accordance with the production rate of the machine. Consequently, it is virtually impossible to determine if the scrap rate is acceptable strictly by the quantity of rejected cans deposited in the scrap can box within a specified time interval. Additionally, slow changes in the scrap rate do not present an identifiable increase over an extended period. For example, a four or five fold increase in the scrap rate over a several month period may not trigger a recognizable increase to an employee assigned to empty the rejected can box.
Consequently, it is advantageous to provide a monitoring system for identifying significant changes in scrap rate as well as providing information as to whether the problem exists in the can manufacturing process or within the can testing machine itself, and the nature of the particular problem.